patch 8.2.0256: time and timer related code is spread out

Problem:    Time and timer related code is spread out.
Solution:   Move time and timer related code to a new file. (Yegappan
            Lakshmanan, closes #5604)
diff --git a/src/proto.h b/src/proto.h
index 7836c52..31f75cf 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -221,6 +221,7 @@
 #  include "textprop.pro"
 # endif
 # include "testing.pro"
+# include "time.pro"
 # include "ui.pro"
 # include "undo.pro"
 # include "usercmd.pro"